Christiane Arnold

Laminin α5 chain is required for intestinal smooth muscle development

Laminins (comprised of alpha, beta, and gamma chains) are heterotrimeric glycoproteins integral to all basement membranes. The function of the lammin alpha5 chain in the developing intestine was defined by analysing laminin alpha5(-/-) mutants and by grafting experiments. We show that lammin alpha5 plays a major role in smooth muscle organisation and differentiation, as excessive folding of intestinal loops and delay in the expression of specific markers are observed in laminin alpha5(-/-) mice. In the subepithelial basement membrane, loss of alpha5 expression was paralleled by ectopic or accelerated deposition of laminin alpha2 and alpha4 chains; this may explain why no obvious defects were observed in the villous form and enterocytic differentiation. This compensation process is attributable to mesenchyme-derived molecules as assessed by chick/mouse alpha5(-/-) grafted associations. Lack of the laminin alpha5 chain was accompanied by a decrease in epithelial alpha3beta1 integrin receptor expression adjacent to the epithelia] basement membrane and of Lutheran blood group glycoprotein in the smooth muscle cells, indicating that these receptors are likely mediating interactions with laminin alpha5-containing molecules. Taken together, the data indicate that the laminin alpha5 chain is essential for normal development of the intestinal smooth muscle and point to possible mesenchyme-derived compensation to promote normal intestinal morphogenesis when laminin alpha5 is absent

Tenascin-C Downregulates Wnt Inhibitor Dickkopf-1, Promoting Tumorigenesis in a Neuroendocrine Tumor Model

The extracellular matrix molecule tenascin-C (TNC) is a major component of the cancer-specific matrix, and high TNC expression is linked to poor prognosis in several cancers. To provide a comprehensive understanding of TNCs functions in cancer, we established an immune-competent transgenic mouse model of pancreatic β-cell carcinogenesis with varying levels of TNC expression and compared stochastic neuroendocrine tumor formation in abundance or absence of TNC. We show that TNC promotes tumor cell survival, the angiogenic switch, more and leaky vessels, carcinoma progression, and lung micrometastasis. TNC downregulates Dickkopf-1 (DKK1) promoter activity through the blocking of actin stress fiber formation, activates Wnt signaling, and induces Wnt target genes in tumor and endothelial cells. Our results implicate DKK1 downregulation as an important mechanism underlying TNC-enhanced tumor progression through the provision of a proangiogenic tumor microenvironment.

Overexpression of laminin α1 chain in colonic cancer cells induces an increase in tumor growth

Laminins represent a growing family of glycoproteins constituting the basement membrane. They are known to direct many biological processes. With respect to carcinogenesis, laminins play an important role in cell adhesion, mitogenesis, differentiation and even metastasis. To further study the biological significance of laminin‐1 (composed of α1, β1 and γ1 chains) in intestinal cell differentiation or tumorigenesis, an α1‐laminin expression vector was introduced into the HT29 colonic cancer cells, in which laminin α1 chain is not expressed. Upon transfection of the α1 chain, the α1β1γ1 trimer was found secreted in the media along with free α1 chain as assessed by immunoprecipitation. The presence of the laminin α1 chain did not significantly modify the levels of the other laminin chains nor the integrins expressed by the HT29 cells. In spite of similar growth properties with the control cells in vitro (plastic dish, soft agar), the laminin α1 transfectants showed a significantly increased tumor growth when injected in nude mice. Histologic and immunohistochemic examination of the laminin α1‐expressing tumors points to an increased recruitment of the host stromal and vascular cells, without modification in the differentiation profile and invasion potential. In parallel, a clear accumulation of laminin‐10 (α5β1γ1) at the carcinoma/stromal interface and a segregation of the integrin β4 subunit at the basal pole of the cancer cells occurred, compared to control tumors. Overall, our observations emphasize the importance of laminin‐1 as a chemoattractant of both stromal and vascular cells and in epithelial/stromal cell interactions for the organization of the basement membrane and segregation of integrins leading to an epithelial cell growth signal. Such a sequence of events is reminiscent of what occurs during development.

Clinical impact of the 2010–2012 low-end shift of high-sensitivity cardiac troponin T

Background: The clinical implications of the 2010–2012 low-end shift of high-sensitivity cardiac troponin T (hs-cTnT) regarding possible misdiagnosis of acute myocardial infarction are largely unknown. Methods: We aimed to quantify the impact of the 2010–2012 low-end shift and adjustment issue in 857 patients presenting to the emergency department with suspected acute myocardial infarction by comparing measurements performed with affected 2010–2012 lots with recalculated 2010–2012 values using a linear regression formula (provided by the manufacturer) and the corrected assay (re-measured in 2013). The final diagnosis was adjudicated by two independent cardiologists using all information including coronary angiography, echocardiography and serial hs-cTnT levels (with the corrected 2013 assay). Results: Acute myocardial infarction was the adjudicated diagnosis in 195 patients (22.7%). Median hs-TnT values were 8.5 ng/l for affected lots, 11.1 ng/l with recalculated and 10 ng/l with the corrected assay (P<0.001 for all comparisons). Spearman correlation coefficient was 0.937 (<0.001) for correct and affected respective correct and recalculated values. The Cusum test indicated significant deviation from linearity (P<0.01) for both correlations. Deviations nearly exclusively affected hs-cTnT levels below the 99th percentile (14 ng/L). Among the 195 patients with an adjudicated diagnosis of acute myocardial infarction, no patient was misclassified using affected lots if using conventional serial sampling. In contrast, misdiagnosis of acute myocardial infarction was significantly increased by affected lots if applying the novel ESC 0 h/1 h algorithm for the early rule-out of acute myocardial infarction (negative predictive value with affected lots 97.7% versus 99.7% with corrected lots). Conclusion: The 2010–2012 hs-cTnT low-end shift affected nearly exclusively levels below the 99th percentile cut-off. While it did not affect the diagnosis of acute myocardial infarction when using conventional serial sampling as done in 2010–2012, it would impact on new early rule-out strategies using very low levels of hs-cTnT such as the ESC 0 h/1 h algorithm. Clinical Trials registration: NCT0047058, NCT00470587

Abnormal Wnt and PI3Kinase Signaling in the Malformed Intestine of lama5 Deficient Mice

Laminins are major constituents of basement membranes and are essential for tissue homeostasis. Laminin-511 is highly expressed in the intestine and its absence causes severe malformation of the intestine and embryonic lethality. To understand the mechanistic role of laminin-511 in tissue homeostasis, we used RNA profiling of embryonic intestinal tissue of lama5 knockout mice and identified a lama5 specific gene expression signature. By combining cell culture experiments with mediated knockdown approaches, we provide a mechanistic link between laminin α5 gene deficiency and the physiological phenotype. We show that laminin α5 plays a crucial role in both epithelial and mesenchymal cell behavior by inhibiting Wnt and activating PI3K signaling. We conclude that conflicting signals are elicited in the absence of lama5, which alter cell adhesion, migration as well as epithelial and muscle differentiation. Conversely, adhesion to laminin-511 may serve as a potent regulator of known interconnected PI3K/Akt and Wnt signaling pathways. Thus deregulated adhesion to laminin-511 may be instrumental in diseases such as human pathologies of the gut where laminin-511 is abnormally expressed as it is shown here.

The laminin response in inflammatory bowel disease: protection or malignancy?

Laminins (LM), basement membrane molecules and mediators of epithelial-stromal communication, are crucial in tissue homeostasis. Inflammatory Bowel Diseases (IBD) are multifactorial pathologies where the microenvironment and in particular LM play an important yet poorly understood role in tissue maintenance, and in cancer progression which represents an inherent risk of IBD. Here we showed first that in human IBD colonic samples and in murine colitis the LMα1 and LMα5 chains are specifically and ectopically overexpressed with a concomitant nuclear p53 accumulation. Linked to this observation, we provided a mechanism showing that p53 induces LMα1 expression at the promoter level by ChIP analysis and this was confirmed by knockdown in cell transfection experiments. To mimic the human disease, we induced colitis and colitis-associated cancer by chemical treatment (DSS) combined or not with a carcinogen (AOM) in transgenic mice overexpressing LMα1 or LMα5 specifically in the intestine. We demonstrated that high LMα1 or LMα5 expression decreased susceptibility towards experimentally DSS-induced colon inflammation as assessed by histological scoring and decrease of pro-inflammatory cytokines. Yet in a pro-oncogenic context, we showed that LM would favor tumorigenesis as revealed by enhanced tumor lesion formation in both LM transgenic mice. Altogether, our results showed that nuclear p53 and associated overexpression of LMα1 and LMα5 protect tissue from inflammation. But in a mutation setting, the same LM molecules favor progression of IBD into colitis-associated cancer. Our transgenic mice represent attractive new models to acquire knowledge about the paradoxical effect of LM that mediate either tissue reparation or cancer according to the microenvironment. In the early phases of IBD, reinforcing basement membrane stability/organization could be a promising therapeutic approach.

Effects of hemolysis on the diagnostic accuracy of cardiac troponin I for the diagnosis of myocardial infarction

Effects of hemolysis on the diagnostic accuracy of cardiac troponin I for the diagnosis of myocardial infarction Christian Puelacher , Raphael Twerenbold , Tamina Mosimann , Jasper Boeddinghaus , Maria Rubini Gimenez , Karin Wildi , Cédric Jaeger , Tobias Reichlin , Jeannine Schneider , Ursina Honegger , Wagener Max , Carmela Schumacher , Thomas Nestelberger , Petra Hillinger , Karin Grimm , Philipp Kreutzinger , Zoraida Moreno Weidmann , Katharina Rentsch , Christiane Arnold , Stefan Osswald , Christian Mueller a,b,⁎